This is the second year progress report for the proposed study of human MHC role in viral immune reactions. We have studied the effect of human serum pool, serum albumin or serum immunoglobulin G (IgG) on mixed lymphocyte reactions (MLR) in a one way mixed lymphocyte culture (MLC). IgG was found to have inhibitory effect at high concentration (0.5%) and enhancing effect at low concentration (0.01%) on the proliferative responses. Two aspects of MLR were also studied; namely, antibody forming cells and proliferative responses, using influenza virus infected stimulators (both autologous and allogeneic). Cell mediated lympholysis (CML) assays is currently carried out with two approaches. One is to maintain cytotoxic T lymphocytes (CTLs) with T cell growth factors (TCGF), so that larger amount of CTLs will be available for the detailed study. Another approach is to remove natural killing (NK) effectors from CTLs generated in Macro MLCs. We are successful in removing NK effectors by K562 monolayers and the HLA specificity recognized by CTLs have been improved.